1. Field
The present disclosure relates to a differential pressure water electrolysis apparatus.
2. Description of the Related Art
In general, hydrogen is used as a fuel gas used for a power-generation reaction in a fuel cell. The hydrogen is generated by, for example, a water-electrolysis apparatus. Since a water-electrolysis apparatus generates hydrogen (and oxygen) by electrolyzing water, the water-electrolysis apparatus uses a solid polymer electrolyte membrane (ion exchange membrane).
Electrode catalyst layers are formed on two surfaces of a solid polymer electrolyte membrane in such a manner as to form an electrolyte membrane/electrode structure, and a current collector is disposed on each side of the electrolyte membrane/electrode structure to form a water electrolysis cell.
In a water electrolysis apparatus that includes a plurality of water electrolysis cells stacked on top of one another, a voltage is applied to the ends of the water electrolysis apparatus in the direction in which the water electrolysis cells are stacked on top of one another, and water is supplied to an anode current collector of each of the water electrolysis cells. Accordingly, the water is decomposed on an anode side of an electrolyte membrane/electrode structure of each of the water electrolysis cells, resulting in generation of hydrogen ions (protons), which move to a cathode side by passing through a solid polymer electrolyte membrane and combine with electrons in a cathode current collector, so that hydrogen is generated. On the anode side, oxygen generated along with the hydrogen is discharged from each of the water electrolysis cells with surplus water.
An example of this type of water electrolysis apparatus is a differential pressure water electrolysis apparatus that generates, by water electrolysis, oxygen on an anode side and generates high-pressure hydrogen having a pressure higher than that of the oxygen on a cathode side. In the case of such a differential pressure water electrolysis apparatus, there is a problem in that high-pressure hydrogen is likely to separate a solid polymer electrolyte membrane and a cathode current collector from each other, which in turn leads to a decrease in electrolysis efficiency.
Accordingly, for example, a high-pressure-hydrogen generation apparatus disclosed in Japanese Unexamined Patent Application Publication No. 2008-121086 is known. This high-pressure-hydrogen generation apparatus includes a piston, which presses a cathode separator against a cathode current collector and a solid polymer electrolyte membrane, and a cylinder that accommodates the piston in such a manner that the piston is able to be freely moved into and out of the cylinder. A cathode-side fluid path and the cylinder are connected by a connection path, and a portion of high-pressure hydrogen gas generated in the cathode-side fluid path is introduced into the cylinder. An elastic body that urges the piston in a direction toward the solid polymer electrolyte membrane is disposed in the cylinder.
A pressure-receiving area of the piston that receives the pressure from the high-pressure hydrogen gas in the cylinder, the area of a surface of the cathode separator, the surface being in contact with the solid polymer electrolyte membrane, and stress that acts on the elastic body are adjusted. Thus, the space between the solid polymer electrolyte membrane and the cathode current collector may be minimized, and improved electrolysis efficiency may be obtained.